1. Prior Art
The prior art appears to be best exemplified by the following patents which were developed in a search:
______________________________________ Hainsworth 2,798,855 July 9, 1957 Hainsworth 2,798,856 July 9, 1957 Carumpalos 3,288,718 Nov. 29, 1966 Edenbaum 3,311,084 March 28, 1967 Edenbaum 3,360,339 Dec. 26, 1967 Verses 3,704,096 Nov. 28, 1972 Chapman 3,862,824 Jan. 28, 1977 Banczak 4,021,252 May 3, 1977 ______________________________________
2. Field of the Invention
Metal cans constitute a very widely utilized medium for the protective packaging of a great variety of products, many millions of cans being used daily for packaging of foods, beverages and many other materials. For many years, the common metal can was constructed of tinplated steel, and was customarily referred to in the industry as an ETP can, the initials standing for "electro-tin-plated." Containers of this type are referred to by the public at large as "tin cans." In recent years, however, the metal can industry has developed organic polymeric resinous coatings for metal cans which offer substantially the same protection to the steel as traditional thin coating of metallic tin. These organic resin based coatings have been applied both as a top coat over the traditional thin tin coating and as the sole protective coating composition applied directly to the steel can body and/or end components to yield both resin coated ETP cans and resin coated untinned steel cans which are now referred to in the industry as "tin-free steel" or TFS cans. This invention is directed primarily to ink compositions suitable for printing identifying indicia on the resin coated surfaces of metal cans including TFS and coated ETP cans as well as coated aluminum cans and can components by means of ink jet printing techniques.
Manufacturing and processing concerns which package various products in metal cans have found it highly desirable to print, at some point on the can surface, a series of coded symbols which carry information of interest primarily to the packager, including the particular machine on which the can was packed, the date and time of packing and perhaps even the identity of the machine operator. Such data are useful in case it is necessary to trace any particular can or cans after they have been packed.
Many of the products packaged in metal cans are subjected to conditions of high temperature and high moisture during pasteurization or sterilization procedures carried out before or after the can is filled with product and sealed. In order to be commercially satisfactory, the coded indicia printed on the cans must be capable of withstanding these processing conditions as well as being resistant to rubbing abrasion.
Another area of interest and need in the art relates to printable sterilization indicators. Such compositions have heretofore utilized pigment combinations, have been applied by contact printing techniques and have been used primarily in determining whether proper sterilization heat has been applied to objects used in medical and surgical procedures. In the manufacturing and processing concerns which package various items in metal cans discussed above, it is highly desirable, in addition to providing coded symbols carrying information of value to the packager, that some means are provided for visually determining when items have been sterilized and/or pasteurized.
The provision of an ink composition which is adapted to a jet printing technique, which is suitable for application to polymer coated surfaces, abrasion resistant and resistant to the high temperature and high moisture during pasteurization or sterilization (while at the same time undergoing a visible and permanent color change when subjected to such processing conditions) is the primary object of this invention. Another object of this invention is to provide a jet ink composition capable of forming markings which show a distinct difference in color among unsterilized and completely sterilized packages.
Further objects of this invention will be apparent from the description of the invention which follows.